Identify a possible reason for the changes in fluid and crystallized intelligence of different age groups in john horn's cross-sectional study.

Fluid intelligence is the capacity to solve a problem which an individual has not confronted before. It analyzes the ability to identify patterns or relationships within the issue and use them in order to solve the problem.

Crystalized intelligence is the capacity to use skills and past experience in order to solve a particular problem. It can be considered as a person's general knowledge or intellect.

Upon the early stages in a person's life, fluid intelligence is highly predominant, due to the fact that the individual has little to none experience.

As a person grows and advances through age groups, the percentage of use of fluid intelligence in comparison to crystalized intelligence starts balancing.

Once a person reaches maturity and enters further age groups, the predominance of his or her use of crystallized intelligence over fluid intelligence is quite clear.  

answer; genetics;

the answer is d.index